Preparation of dimeric contrast agents

Abstract

The present invention relates to a gadolinium dimer contrast agent [μ-[1-[bis[2-(hydroxy-κO)-3-[4,7,10-tris[(carboxy-κO)methyl]-1,4,7,10-tetraazacyclododecan-1-yl-κN 1 ,κN 4 ,κN 7 ,κN 10 The present invention relates to a method for the preparation of the di-gadolinium complex [propyl]amino]-1-deoxy-D-glucitrate(6-)]]. Such a process includes a preparation step carried out in one pot and without isolation of the resulting intermediate. The gadolinium dimer contrast agent can be used in diagnostic imaging, in particular in magnetic resonance imaging (MRI).

Description

[Technical field]

[0001] The present invention relates to a compound that can be used as a contrast agent in magnetic resonance imaging (MRI), the compound [μ-[1-[bis[2-(hydroxy-κO)-3-[4,7,10-tris[(carboxy-κO)methyl]-1,4,7,10-tetraazacyclododecan-1-yl-κN 1 ,κN 4 ,κN 7 ,κN 10 ]propyl]amino]-1-deoxy-D-glucitrate(6-)]]di-gadolinium complex. [Background technology]

[0002] Magnetic resonance imaging (MRI) is a well-known diagnostic imaging technique that is used in clinical diagnosis for an increasing number of indications.

[0003] Gadolinium (Gd(III)) complexes are commonly used as MRI contrast agents due to their long relaxation times.

[0004] WO2017 / 098044 (of the same applicant as the present application) discloses dimeric paramagnetic complexes useful as MRI contrast agents. Among many specific compounds, this application discloses dimeric paramagnetic complexes of the formula [ka] The present invention discloses a di-gadolinium complex of the 1-[bis[2-hydroxy-3-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-1-yl]propyl]amino]-1-deoxy-D-glucitol ligand, represented below as "dimeric complex compound 5" or simply "compound 5". Compound 5 shows interesting properties, especially in terms of relaxivity and tolerability, making it suitable for carrying out in vivo imaging diagnostics at doses of the paramagnetic complex lower than those required for commercially available contrast agents.

[0005] WO2017 / 098044 further discloses the following process (Scheme 1) for synthesizing compound 5. [ka]

[0006] The main steps of the process disclosed in WO2017 / 098044 are: a) preparing and isolating DO3A tri-tert-butyl ester (compound 1A), essentially as disclosed in Org. Synth. 2008, 85, 10; b) Preparation of intermediate 2 by alkylation of D-glucamine with epichlorohydrin (molar ratio 1:4.95) in MeOH at 50° C. for 26 hours and isolating the concentrated product by evaporation of the crude reaction mixture; c) alkylation of DO3A tri-tert-butyl ester with intermediate 2 in DMSO and Et3N, followed by evaporation of the solvent and purification of the crude residue by Amberlite XAD® 1600 to give the protected ligand 3; d) deprotection of ligand 3 using TFA acid and TIPS in dichloromethane, evaporation of the crude reaction mixture and purification of the residue by Amberlite XE 750; e) complexation of ligand 4 by stoichiometric addition of gadolinium chloride hexahydrate in water, filtration of the solution and evaporation of the solvent to obtain a crude product, which is purified on Amberchrome CG161M resin. Includes.

[0007] The process disclosed in WO2017 / 098044 requires the synthesis and isolation of each individual intermediate, which is typically performed by evaporating the solvent to the residue. Such isolation steps are not suitable for large-scale production and inevitably reduce the overall yield and efficiency of the process.

[0008] Furthermore, the processes disclosed in WO2017 / 098044 involve the use of harsh materials such as TFA, TIPS and DCM that are difficult to handle and may cause corrosion and therefore wear on the synthesis equipment and / or may be unsafe for worker health, making them unsuitable for implementation, particularly on a large scale (e.g. industrial processes). Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention generally relates to an optimized process for the preparation of dimeric complex compound 5, which involves a preparation step carried out in one pot, without isolation of the obtained intermediates, thereby allowing both time saving and improving the overall yield and efficiency. [Means for solving the problem]

[0010] More specifically, the present invention relates to a compound having the formula [ka] A method for producing a dimeric complex compound 5 represented by the following steps: a) Formula 1B [ka] wherein X is a halogen anion, preferably selected from the group consisting of chloride, bromide and iodide anions, and y is an integer from 1 to 3, preferably y is 1. a salt of DO3A tri-tert-butyl ester represented by the formula: b) converting salt 1B of step a) to a salt of formula 1A [ka] obtaining a heterogeneous mixture containing DO3A tri-tert-butyl ester represented by: c) recovering the organic solvent from the heterogeneous mixture of step b) to obtain an organic solution containing DO3A tri-tert-butyl ester of formula 1A; d) Equation 2 [ka] preparing a solution comprising a compound represented by the formula: e) Mix the solutions of steps c) and d) to obtain a mixture of the compound represented by formula 3. [ka] obtaining a solution containing a compound represented by f) removing the tert-butyl protecting group from the compound of formula 3 without isolating the compound from the solution of step e) to give a compound of formula 4 [ka] to obtain a solution containing free ligands, each of which is represented by g) adding gadolinium metal ions to the solution of step f) without isolating the free ligand of formula 4 to obtain a solution containing the dimeric complex of formula 5; and h) isolating the dimeric complex. The present invention relates to a method of manufacturing the same.

[0011] In a preferred embodiment of the invention, the reaction solvent in all steps following the preparation of the compound of formula 3 is an aqueous solvent or aqueous solvent mixture, which advantageously does not contain potentially hazardous substances such as TFA, TIPS and / or DCM.

[0012] Steps a)-c) of the process of the present invention generally involve the preparation of a solution containing DO3A tri-tert-butyl ester 1A. In particular, an organic solution containing 1A is prepared by converting protected DO3A salt 1B to protected DO3A 1A, respectively, using two immiscible solvents, as described in detail below.

[0013] Step d) of the process of the present invention comprises the preparation of a compound of formula 2, which can be obtained by alkylation of D-glucamine with epichlorohydrin. The alkylation is carried out in an organic solvent, such as a dipolar organic solvent or an aqueous mixture thereof. Suitable organic solvents include, for example, alcohols such as DMAC, DMF, MeOH, and mixtures thereof. More preferably, the organic solvent is DMAC. Distillation of excess aqueous solvent and / or epichlorohydrin from the mixture provides a solution of the compound of formula 2 in an organic solvent, suitable for use directly in the next step without isolating and / or further purifying the alkylated product.

[0014] Step e) of the process of the present invention involves the condensation (or coupling, as used interchangeably herein) of the intermediate compound of formula 2 with DO3A tri-tert-butyl ester 1A to form the protected ligand of formula 3. The condensation reaction is preferably carried out in the presence of a base, which acts, for example, as an acceptor for the HCl formed. For example, suitable bases include anion exchange resins such as Amberlite GC 400, NMM, tBuOK, Et3N, DIPEA, etc., with Et3N and DIPEA being preferred, and DIPEA being particularly preferred.

[0015] In one embodiment, the condensation reaction is carried out by adding an organic solution comprising a base and DO3A tri-tert-butyl ester 1A recovered directly from step c) to a solution comprising compound 2 recovered from step d) to obtain a crude organic solution comprising the condensation product of formula 3 in an organic solvent mixture. The crude organic solution is then purified to obtain a purified product in a water / organic solvent mixture, and optionally and preferably the organic solvent is finally distilled to obtain the protected ligand of formula 3 in an aqueous solvent or aqueous solvent mixture that can be used directly in the next step without isolation and / or further purification of the protected ligand itself.

[0016] Step f) of the process of the invention essentially involves the removal of the carboxylic acid protecting group from the protected ligand of formula 3 to obtain an aqueous solution or mixture containing the free ligand of formula 4, respectively. Deprotection by hydrolysis of the tert-butyl protecting group can be carried out under both acidic and basic conditions, using reactants and conditions known to those skilled in the art. In one embodiment, the deprotection is carried out by acidifying the aqueous solution or mixture containing the protected ligand directly recovered from step e) of the process, to obtain an acidic solution containing the free ligand of formula 4. The acidification is preferably carried out by addition of an acid, for example selected from HCl, H2SO4 and H3PO4. In a preferred embodiment, the deprotection is carried out with HCl. The aqueous solution or mixture containing the ligand 4 is then recovered by neutralization of the acidic solution, followed by purification and partial concentration of the resulting mixture, and is used directly in the complexation step without isolation.

[0017] Step g) of the process of the present invention comprises complexing the ligand with gadolinium metal ions to obtain the desired dimeric complex 5. The complexation reaction can be conveniently carried out according to known procedures, for example by stoichiometrically adding a suitable Gd(III) derivative, specifically an oxide such as Gd2O3 or a gadolinium salt, to the solution containing the ligand. In one embodiment, the complexation reaction is carried out by adding GdCl3 to the solution containing the ligand directly recovered from step f). The resulting mixture is adjusted to a pH value of about 5 to about 7 and maintained under stirring to obtain an aqueous solution or mixture containing the gadolinium complex 5, which is purified and concentrated to obtain a solution containing the desired dimeric complex 5 with the desired purity.

[0018] Step h) of the process of the present invention is the final isolation of the desired gadolinium complex 5. This step can be conveniently carried out according to known procedures. In one embodiment, the solution containing the purified complex recovered from step g) is spray dried to obtain the desired product as a white solid meeting the required purity specifications.

[0019] Interestingly, the preparation process of the present invention avoids or greatly reduces the use of hazardous reagents such as trifluoroacetic acid (TFA) and hazardous solvents such as dichloromethane, which are required in prior art processes and are difficult to handle when carried out on a large scale, e.g., in an industrial process.

[0020] Furthermore, the process of the present invention includes steps carried out in one pot, making it suitable for large-scale implementation and not requiring isolation of either the prepared precursor (such as 1A) or intermediates. As a result, in addition to facilitating shorter reaction times and being easily implemented on a large scale as described above, the process of the present invention can advantageously significantly improve the overall process yield from 10% (obtained in the process disclosed in WO2017098044) to at least 20%, preferably 25%, typically about 28%, and advantageously greater than 29%. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] As used herein, unless otherwise specified, the term "intermediate" (as used with respect to, for example, a compound of formula 2 resulting from the alkylation reaction of D-glucamine with epichlorohydrin, or a protected ligand of formula 3) includes within its meaning a molecule produced during the chemical synthesis or preparation steps of the present process that is not itself the end product, but requires one (or more) further reactions, e.g., alkylation / deprotection / complexation reactions, to obtain the end product of the present process, i.e., dimeric complex compound 5.

[0022] Unless otherwise specified, the term "precursor" (e.g., as used with respect to compound 1A) includes within its meaning a molecule that participates in a chemical reaction that facilitates the conversion of said precursor into another molecule that contains or is derived from said precursor.

[0023] As used herein, the term "aqueous solvent" includes within its meaning water and aqueous solutions acting as a solvent, such as physiological saline. Aqueous solutions may contain a small amount of organic solvent miscible with water, for example, the volume percentage of organic solvent miscible with water is 10% or less, preferably 8% or less, more preferably 5% or less. Preferably, the aqueous solvent is water.

[0024] The expressions "water / organic solvent mixture" or more simply "aqueous solvent mixture", as used interchangeably herein, refer to a mixture of two or more solvents, including an aqueous solvent, e.g. a mixture of water and one or more organic solvents, which are miscible with each other to give a homogeneous solvent mixture, the volume percentage of one or more organic solvents being higher than 10%, preferably higher than 15%, more preferably higher than 20%. Suitable examples include a mixture of water and acetonitrile (water / MeCN), e.g. used as eluent in the chromatographic purification of the compound of formula 3, or a mixture of water / MeCN / DMAC, e.g. obtained after diluting the crude mixture resulting from the condensation reaction of step e) with water. According to a preferred embodiment of the present invention, the organic solvent or organic solvents of the aqueous solvent mixture (as well as in the aqueous solvent, if present) are not highly hazardous solvents or substances; indeed, the aqueous solvent mixture is preferably free of highly hazardous solvents such as TFA, TIPS and / or DCM.

[0025] Similarly, the expressions "aqueous solution" and "aqueous mixture" respectively include within their meaning a solution or mixture containing water. Suitable examples include solutions containing one or more compounds, e.g., reagents, acids, bases or reaction products, in water (or more generally, in an aqueous mixture), and mixtures such as water / organic mixtures resulting from the addition of water or an aqueous solution to a reaction mixture in an organic solvent or solvent mixture. For example, the term "basic aqueous solution" refers to a solution containing at least a base.

[0026] According to this specification, unless otherwise specified, the term "heterogeneous mixture" refers to a biphasic heterogeneous liquid mixture, i.e. a mixture comprising two liquids that are immiscible with each other.

[0027] It refers to a protecting group that is suitable for retaining the function of the group to which it is attached. In particular, the protecting group is used to retain carboxyl functionality. More specifically, the term refers to the tert-butyl group that retains the chelating function of the carboxyl group of the ligand by forming tert-butyl ester [for general reference on protecting groups and deprotection conditions, see TW Green and PGM Wuts; Protective Groups in Organic Synthesis, Wiley, NY 1999, third edition].

[0028] One embodiment of the present invention essentially corresponds to the following general synthetic scheme 2: [ka] The method for producing the dimer compound 5 shown in The method comprises the following main steps: a)-c) using a biphasic heterogeneous mixture to convert a salt of DO3A tri-tert-butyl ester 1B to DO3A tri-tert-butyl ester 1A, and then recovering the organic phase to obtain an organic solution containing DO3A tri-tert-butyl ester 1A in an organic solvent; d) reacting D-glutamine with epichlorohydrin, optionally in the presence of an organic solvent such as DMAC, to obtain a solution containing the compound of formula 2; and e) reacting the compound of formula 2 obtained in step d) with DO3A tri-tert-butyl ester 1A obtained in step c) in the presence of a base, optionally concentrating the solution to obtain an organic crude, diluting the organic crude with water, an aqueous / organic solvent mixture and / or optionally an aqueous solution to obtain an aqueous / organic crude, purifying the aqueous / organic crude and optionally removing the organic solvent to obtain an aqueous solution or aqueous mixture containing the protected ligand of formula 3; and without isolating the product. f) acidifying the solution containing the protected ligand of formula 3 obtained in step e) to obtain an acidic aqueous solution or aqueous mixture containing the deprotected ligand 4, respectively, neutralizing the acidic solution and purifying the resulting neutral solution to obtain an aqueous solution or aqueous mixture containing the deprotected ligand 4; and g) adding gadolinium metal ions to a solution containing the ligand 4 to obtain a solution containing the corresponding complex compound 5; and h) isolating the complex. Includes.

[0029] Process a) In step a), a heterogeneous mixture can be obtained which contains the salt 1B. Indeed, it has been found that by using such a heterogeneous mixture, it is possible to shorten the reaction time of the conversion step b). In particular, in step a), salt 1B is mixed with an aqueous base solution and an organic solvent immiscible with the aqueous base solution, such that the two immiscible liquids (the aqueous base solution and the organic solvent immiscible with the aqueous base solution) form a heterogeneous mixture, i.e., the heterogeneous mixture comprises both the aqueous base solution, the organic solvent, and salt 1B.

[0030] Salt 1B has the formula [ka] (wherein X is a halogen anion and y is an integer from 1 to 3). According to a preferred embodiment, y is 1 and / or X is a bromide ion (Br - According to a more preferred embodiment, y is 1 and X is a bromide ion (Br - ) and salt 1B is DO3A 3t-Bu-HBr.

[0031] Salt 1B can be obtained according to known methods. For example, as disclosed in detail in WO2021116165, salt 1B can be advantageously obtained by the following steps: I) reacting cyclen (1,4,7,10-tetraazacyclododecane) with an acetate of formula XCHOOtBu, where X is as defined above, in an organic solvent in the presence of an auxiliary base to obtain a mixture; II) adding water to the mixture of step I), preferably in an amount of 2.5 to 10 times w / w relative to the amount of cyclen in step I), to obtain a suspension of salt 1B; and III) Recovering and washing the salt 1B.

[0032] According to a preferred embodiment, the organic solvent immiscible with aqueous basic solutions is an ether, such as methyl tert-butyl ether (MTBE). These ethers immiscible with aqueous basic solutions have been found to be particularly effective for the conversion of salt 1B in conversion step b).

[0033] According to a preferred embodiment, the amount of the organic solvent in step a) is 1.0 to 5.0 w / w, preferably 1.2 to 3.0 w / w, more preferably 1.4 to 1.6 w / w, and even more preferably 1.5 w / w, relative to the amount of salt 1B.

[0034] The basic aqueous solution comprises a base, which is preferably an inorganic base, for example an inorganic base selected from the group consisting of KOH, NaOH, Na2CO3 and K2CO3. Such base may preferably be present in a molar ratio of 1.0 to 4.0 moles, preferably 1.2 to 3.0 moles, more preferably 1.7 to 2.3 moles, and even more preferably 2.0 moles, relative to 1 mole of salt 1B. These molar ratios have been found to be particularly effective for the conversion of salt 1B in conversion step b), especially when salt 1B has y=1. When salt 1B has y=2 or 3, the amount of basic aqueous solution is preferably higher than the amounts described above, particularly preferably 2 or 3 times higher than the amounts described above when y is 1, respectively.

[0035] According to a preferred embodiment, the amount of the basic aqueous solution in step a) is 2.0 to 10 w / w, preferably 2.2 to 6.0 w / w, more preferably 2.8 to 3.2 w / w, and even more preferably 3.0 w / w, relative to the amount of salt 1B.

[0036] The heterogeneous mixture obtained in step a) is used as is (ie without separating salt 1B from the heterogeneous mixture) in the subsequent conversion step b).

[0037] Step b) Step b) converts salt 1B into DO3A tri-tert-butyl ester 1A. Specifically, in step b), salt 1B is converted into the corresponding DO3A tri-tert-butyl ester 1A by the basic condition of a basic aqueous solution. Since DO3A tri-tert-butyl ester 1A is more soluble in an organic solvent than in a basic aqueous solution, the converted DO3A tri-tert-butyl ester 1A can be found to be solubilized in the organic solvent.

[0038] Step b) is a reaction that takes place in a heterogeneous (two-phase) medium and is therefore preferably carried out for a period of less than 5 hours, more preferably from 1 to 5 hours, even more preferably from 1.5 to 3 hours, and most preferably for 2 hours, preferably by stirring the heterogeneous mixture obtained by step a) to increase the interaction between the two phases.

[0039] According to one embodiment, step b) comprises adjusting and / or maintaining the temperature in the range of 15-50°C, preferably in the range of 20-30°C, more preferably in the range of 23-27°C, and even more preferably in the range of 25°C, for the time period disclosed above, for example with stirring. The heterogeneous mixture comprising DO3A tri-tert-butyl ester 1A obtained according to step b) is advantageously used as such in the following step c).

[0040] Process c) Step c) recovers the organic solvent from the heterogeneous mixture of the previous step b). As described above, DO3A tri-tert-butyl ester 1A can be found to be solubilized in the organic solvent, so that recovering the organic solvent corresponds to obtaining an organic solution containing DO3A tri-tert-butyl ester 1A. This recovery step c) can be carried out according to known methods, for example by discarding the basic aqueous medium from the heterogeneous mixture.

[0041] After step c) and before step e), the organic solution containing DO3A tri-tert-butyl ester 1A is subjected to a solvent change step, changing the solvent to another organic solvent found to be more suitable and efficient for the condensation step e). Specifically, after step c) and before step e), the organic solution containing DO3A tri-tert-butyl ester 1A is preferably subjected to a solvent exchange step to obtain an organic solution of DO3A tri-tert-butyl ester 1A, the organic solvent comprising MeCN or a C2-C4 alcohol, preferably isopropanol. According to a preferred embodiment, when the organic solution is an ether such as MTBE, the solvent change step comprises (i) adding MeCN or a C2-C4 alcohol, preferably isopropanol, to the organic solution, and (ii) removing the ether from the organic solution by distillation, whereby the organic solvent of the organic solution containing DO3A tri-tert-butyl ester 1A comprises MeCN or a C2-C4 alcohol, preferably isopropanol. When the solvent change step is carried out by addition of a C2-C4 alcohol, preferably isopropanol, such alcohol is added in an amount of preferably 0.4-0.8 w / w, more preferably 0.5-0.7 w / w, relative to the amount of DO3A tri-tert-butyl ester 1A.

[0042] After step c) and before step e), e.g. after the solvent exchange step disclosed above, the organic solution containing DO3A tri-tert-butyl ester 1A preferably has a concentration of 40-80% w / w, preferably 50-70% w / w, more preferably 56-63% w / w. Such a concentration can be obtained by conventional means, e.g. by concentrating the organic solution, e.g. by evaporating the solvent. The above concentration ranges have been found to improve the conjugation reaction of step e).

[0043] Step d) This step involves reacting D-glucamine with epichlorohydrin to prepare a solution of the intermediate compound of formula 2. In one embodiment, the reaction is carried out in a mixture of solvents, preferably water / DMAC, by using a slight stoichiometric excess of epichlorohydrin, for example 2-3, more preferably about 2.2 moles of epichlorohydrin per mole of D-glucamine. Preferably, the reaction of step d) is carried out by using a slight stoichiometric excess of epichlorohydrin, for example 2-3, more preferably 2.05-2.5, even more preferably about 2.2 moles of epichlorohydrin per mole of D-glucamine.

[0044] In a preferred embodiment, step d) of the manufacturing method comprises: d1) adding an aqueous solution of D-glucamine to a solution of epichlorohydrin in DMAC to obtain the intermediate compound of formula 2 in a water / DMAC solvent mixture; and d2) removing water from the solvent mixture to obtain a solution of the compound of formula 2 in the organic solvent. Includes.

[0045] The addition of D-glucamine to the epichlorohydrin solution is preferably carried out at room temperature over a period of about 2 hours to obtain a mixture, which is then maintained under stirring at a temperature of 15 to 30°C, preferably 15 to 25°C, more preferably 20 to 25°C, for 16 to 24 hours, preferably 16 to 20 hours, more preferably about 17 hours.

[0046] The mixture is then distilled to remove water and possibly epichlorohydrin residues. Distillation is preferably carried out under reduced pressure at a temperature preferably between 40-65° C. to obtain a solution of the desired intermediate compound of formula 2 in DMAC, preferably with a residual water content of <2% w / w. The resulting solution is used directly in the subsequent condensation reaction without the need for product isolation or purification.

[0047] Step d) and steps a) to c) can be performed in parallel, or can be performed in any order (e.g., steps a) to c) can be performed first and then step d), or step d) can be performed first and then steps a) to c).

[0048] Process e) This step essentially involves the condensation of DO3A tri-tert-butyl ester 1A with intermediate 2 in the presence of a base such as Et3N, or more preferably DIPEA. The condensation is preferably carried out by combining a solution of ester 1A in a base and MeCN or a C2-C4 alcohol (such as isopropanol) recovered from step c) with a solution of intermediate 2 in DMAC recovered directly from step d), to obtain a raw solution (or crude) containing the protected ligand of formula 3 in a mixture of MeCN / DMAC or alcohol / DMAC organic solvents, which is then purified.

[0049] In one embodiment, the organic crude solution resulting from the condensation reaction is diluted with water or partially concentrated and then diluted with water or an aqueous solvent mixture, preferably water / MeCN, to obtain an aqueous / organic crude, or aqueous crude, as used interchangeably herein.

[0050] In a preferred embodiment, the aqueous / organic crude thus obtained, or preferably the organic crude resulting from the condensation reaction, is added with an aqueous solution which induces the precipitation of the reaction salt containing DO3A tri-tert-butyl ester hydrochloride, and the precipitate is then removed by filtration to obtain an aqueous / organic filtrate. The aqueous / organic crude or aqueous / organic filtrate is then preferably purified by chromatography.

[0051] In one embodiment, the aqueous solution used to facilitate precipitation of the hydrochloride salt is aqueous ammonia.

[0052] More specifically, step e) of the present manufacturing method preferably comprises: e1) condensing the intermediate compound of formula 2 obtained in step d) with DO3A tri-tert-butyl ester 1A obtained in step c) in the presence of a base, preferably DIPEA, to obtain a crude organic solution comprising the condensation product of formula 3 and a reaction salt in an organic solvent mixture, and optionally concentrating the crude organic solution; e2) diluting the organic crude of step e1) with water or a water / organic solvent mixture, preferably water / MeCN, to obtain an aqueous / organic crude; e3) optionally adding to the aqueous / organic crude an aqueous solution which induces precipitation of the reaction salt and removing the precipitate by filtration to obtain an aqueous / organic filtrate; or e4) diluting the organic crude product of step e1) with an aqueous solution that promotes precipitation of the reaction salt and removing the precipitate by filtration to obtain an aqueous / organic filtrate solution; e5) purifying the aqueous / organic crude product of step e2) or the aqueous / organic filtrate of step e3) or e4) to obtain a solution of the protected ligand of formula 3 in an aqueous / organic solvent mixture that may be used in the subsequent deprotection step without the need for isolation or further purification of the protected product; and e6) Optionally removing the organic solvent from the mixture to obtain a solution of the protected ligand of formula 3 in water, or more generally in an aqueous solvent, which is used in the subsequent deprotection step without the need for isolation or further purification of the protected product. Includes.

[0053] The condensation reaction is preferably carried out by adding a solution of ester 1A in a base and MeCN or a C2-C4 alcohol (e.g., isopropanol) recovered from step c) of the present process to a solution of the intermediate compound of formula 2 in DMAC recovered from step d).

[0054] The suitable amounts of base and ester 1A are conveniently determined relative to the amount of D-glucamine to be reacted. In one embodiment, the condensation reaction is carried out by using 1.6-2.4 moles, preferably about 1.8 moles, of ester 1A and 2-4 moles, preferably about 2.3 moles, of DIPEA per mole of starting D-glucamine to be reacted.

[0055] The addition is preferably carried out at a temperature of 40-50° C. The condensation reaction is then carried out at a temperature of 50-80° C., preferably 65-75° C., for example for 60-80 hours, preferably 70-75 hours, to obtain a stock solution containing the desired condensation product of formula 3 and the hydrochloride salt in a MeCN / DMAC or alcohol / DMAC solvent mixture.

[0056] In one embodiment, the stock solution is then diluted with water, preferably to obtain an aqueous / organic crude having a concentration of about 25-30%, more preferably about 25% (w / w). In a preferred embodiment, the aqueous crude contains an amount of water, by weight, at least equal to the amount of organic solvent in the mixture, specifically MeCN; more preferably, the crude has a water:MeCN ratio of about 60:40.

[0057] The aqueous / organic crude is then preferably purified by chromatography, more preferably on a resin, even more preferably on an adsorptive resin such as Amberlite XAD® 1600. In a preferred embodiment, the aqueous crude is purified on an adsorptive resin such as Amberlite XAD® 1600 by using a water / MeCN mixture as eluent, making it possible to obtain both the unreacted DO3A tri-tert-butyl ester 1A and the pure condensation product as separate fractions in a water / MeCN solvent mixture.

[0058] In another embodiment, the raw solution resulting from the condensation reaction is first concentrated by removing at least MeCN, for example by distillation. The concentrated solution can then be diluted with water or a mixture of water:MeCN to obtain an aqueous / organic crude having the water:MeCN ratio described above, which is then purified by chromatography as described above.

[0059] If the stock solution obtained from the condensation reaction consists of alcohol / DMAC as the solvent mixture, the alcohol can be removed (e.g., by distillation) and the resulting solution can then be diluted with water or a mixture of water:MeCN to obtain an aqueous / organic crude product having the above water:MeCN ratio, which is then purified by chromatography as described above.

[0060] Optionally, the aqueous / organic crude obtained as described above may be added with an aqueous solution such as aqueous ammonia, which, upon cooling of the mixture, induces the precipitation of unreacted DO3A tri-tert-butyl ester as the hydrochloride salt, which may then be removed by filtration and recycled. The filtrate solution, freed of most of the chloride salt, is then purified by chromatography as described above on an adsorptive resin such as Amberlite XAD® 1600 resin to obtain the residual DO3A tri-tert-butyl ester 1A and the pure condensation product as separate fractions in an aqueous / organic solvent mixture such as water / MeCN.

[0061] In a preferred embodiment, an aqueous solution, e.g., containing aqueous ammonia, is added directly to the organic stock solution resulting from the condensation reaction, and cooling of the mixture induces precipitation of unreacted DO3A tri-tert-butyl ester as the hydrochloride salt, which may then be removed by filtration and recycled. The filtrate, freed of most of the chloride salt, is then purified by chromatography on an adsorptive resin, such as Amberlite XAD® 1600 resin, as described above, to obtain the residual DO3A tri-tert-butyl ester 1A and the pure condensation product as separate fractions in an aqueous / organic solvent mixture, such as water / MeCN.

[0062] Optionally, final distillation of organic solvent from the pure fractions, e.g. under reduced pressure, gives the condensation product of formula 3 in aqueous solution with a final concentration of 5-15% (w / w), preferably about 10% (w / w), which is suitable for direct use in the subsequent deprotection step without the need for isolation or further purification of intermediates.

[0063] Interestingly, the steps of the procedure described above allow the protected condensation product 3 to be obtained in an aqueous solvent or aqueous solvent mixture, thus making it possible to carry out its deprotection and complexation to the final complex 5 by using water, more generally an aqueous solvent or an aqueous solvent mixture, as one of the only or main reaction solvents. The protected condensation product 3 in an aqueous solvent can be obtained by various methods known to those skilled in the art. For example, the organic crude solution of the compound of formula 3, obtained for example by reacting the compound of formula 2 obtained in step d) with DO3A tri-tert-butyl ester 1A obtained in step c), as described above, can be diluted with water, an aqueous / organic solvent mixture, or an aqueous solution to obtain an aqueous / organic crude. Before removing the organic solvent, the aqueous / organic crude can be purified via chromatography, preferably a resin, more preferably an adsorbent resin such as Amberlite XAD® 1600. The organic solvent can then be removed to obtain an aqueous solution of the compound of formula 3, for example by distillation under reduced pressure. The protected condensation product 3 in an aqueous solvent mixture can also be obtained by various methods known to those skilled in the art. For example, the crude organic solution of the compound of formula 3 obtained by reacting the compound of formula 2 obtained in step d) with DO3A tri-tert-butyl ester 1A obtained in step c) can be diluted with water, a water / organic solvent mixture, or an aqueous solution, resulting in an aqueous / organic solution for use in the subsequent step without isolating the product 3.

[0064] Thus, according to a preferred embodiment of the invention, the invention comprises the further step of converting the solution of the compound of formula 3 into an aqueous solution of the compound of formula 3, or into an aqueous mixture of the compound of formula 3. Preferably, this further step is carried out by: (i) diluting the solution of the compound of formula 3 with water, a water / organic solvent mixture, or an aqueous solution to obtain an aqueous mixture (or a water / organic solution), and (ii) optionally removing the organic solvent, for example by distillation, to obtain an aqueous solution.

[0065] Process f) This step involves deprotecting the protected ligand of formula 3 by removing the carboxyl protecting group to obtain an aqueous solution or mixture of the free ligand 4. This reaction is preferably carried out by acidifying the aqueous solution or mixture containing the protected ligand of formula 3 directly recovered from step e) of the present process. In one embodiment, step f) of the manufacturing method comprises: f1) adding an acid to the aqueous solution or mixture of the compound of formula 3 recovered from step e) to obtain an acidic solution of free ligand 4; f2) adding a base to the acidic solution to obtain a substantially neutralized solution of Ligand 4; and f3) Purification and optional subsequent concentration of the neutralized solution gives an aqueous solution or mixture containing the free ligand 4 which can be used directly in a subsequent complexation reaction without the need for ligand isolation.

[0066] In one embodiment, the solution containing the protected compound of formula 3 is acidified by the addition of an acid, for example, 34% aqueous HCl. The acidification is carried out using a large excess of HCl (for example, 30-100 times, preferably 30-80 times, more preferably 40-50 times the molar amount of the protected compound 3).

[0067] The acid is added at a temperature of 20 to 35° C., preferably 30 to 35° C. The resulting solution is then maintained under stirring at 30 to 40° C. for 10 to 36 hours, preferably 25 to 30 hours, and the ligand is deprotected, for example, by chromatography.

[0068] The acidic solution is then cooled, for example to 25° C., and neutralized by the addition of a base, preferably NaOH, to obtain a stock solution with a final pH of 6.5 to 7.5, which is then purified.

[0069] Preferably, the purification steps include: i) distilling the neutralized solution to remove the produced t-butanol; ii) desalting the distillation residue; and iii) purifying the desalted solution by chromatography.

[0070] In particular, in one embodiment, the solution obtained by the addition of the base is first distilled to remove the tert-butanol formed, preferably at a temperature of 40-60° C. The distillation residue is then desalted, preferably by nanofiltration, to purify the recovered solution.

[0071] In one embodiment, the solution obtained by nanofiltration is first concentrated under reduced pressure, for example at 40-60° C., preferably at about 50° C., to a concentration preferably of 23-27% (w / w), and then purified by elution on a resin, more preferably Amberlite XAD® 1600. The eluate is optionally treated with activated carbon, such as Carboprone 4N, and concentrated under reduced pressure at about 50° C., to obtain an aqueous solution or mixture containing the ligand of formula 4, preferably in a final concentration of 8-25%, which is used directly in the subsequent complexation reaction without isolation of the ligand.

[0072] Advantageously, the above procedure involves the use of water as the sole or one of the main reaction solvents, thereby avoiding or reducing the use of organic solvents, particularly hazardous solvents such as DCM, which are required in the above-mentioned prior art processes, and hazardous reactants such as TFA, TIPS, etc. These hazardous materials are difficult to handle and not suitable for large-scale production. Moreover, the process provides the desired ligand in an aqueous solution or mixture, which can be used directly in the complexation reaction without the need for isolation.

[0073] Process g) The process involves complexing a dimeric ligand of formula 4 with gadolinium ions to obtain an aqueous solution or mixture containing the desired chelate complex 5. More specifically, the method preferably includes the following steps: g1) adding a gadolinium salt, such as GdCl3, to the solution containing the ligand recovered from step f) to obtain a mixture containing the dimeric chelate complex 5; g2) adding a base to obtain a mixture with a pH of about 5 to about 7; g3) purifying the mixture to obtain a solution containing the dimeric complex of formula 5; and g4) Concentrate the recovered solution.

[0074] This reaction is preferably carried out by adding GdCl3 directly to the solution containing the ligand recovered in the previous step. The addition is preferably carried out at a temperature between 25 and 45° C. The amount of GdCl3 required to comprehensively complex the ligand is determined by titration of the Gd solution according to known procedures, for example with copper sulfate as titrant.

[0075] In one embodiment, the ratio of the ligand of formula 4 to the added GdCl3 is 1:1.98 to 1:2.02 (mol / mol), more preferably 1:2.00 to ensure consumption of the added lanthanide ion.

[0076] After the addition, the pH of the resulting mixture is adjusted to a range of about 5 to about 7.5 by the addition of a base, preferably NaOH.

[0077] For example, in one embodiment, GdCl3 is added to the ligand solution at a temperature of, for example, 20-25° C. The resulting mixture is adjusted to pH 7-7.5, for example, about pH 7, by addition of NaOH, and then maintained under stirring at 20-25° C. for about 25 hours to achieve exhaustive complexation of the ligand.

[0078] In another embodiment, GdCl3 and an amount of NaOH required to maintain the pH at the desired neutral value are added simultaneously, and the mixture is maintained with stirring as above for about 25 hours.

[0079] In a preferred embodiment, the mixture obtained by adding GdCl3 is adjusted to a pH of about 5 to about 6, preferably 5 to 5.6, more preferably about 5.3, and then maintained at about 40°C with stirring for 1 to 4 hours, for example, about 2 hours. Then, free Gd 3+ The presence of remaining free species, such as ligand or partially complexed ligand, is assessed, for example, by titration and / or HPLC methods and corrected by adding a calculated amount of ligand or GdCl3 to obtain an aqueous solution or mixture containing the dimeric complex of formula 5, which is then purified.

[0080] Purification is preferably carried out by chromatography, preferably on a resin.

[0081] In one embodiment, purification involves eluting the mixture resulting from the complexation reaction with a polymeric resin, preferably Amberlite XAD® 1600 resin.

[0082] In another embodiment, purification comprises a first elution of the mixture resulting from the complexation reaction with a chelating resin, for example selected from Hi Trap IMAC FF, Lewatit MonoPlus TP 260, Lewatit TP 208, IRC748I, DIAION CR11, SiliaMets AMPA and SiliaMets DOTA, preferably Diaion CR11 and Amberlite IRC748, to minimize the free gadolinium content and to allow further purification of the collected eluate with a polymeric resin, such as Amberlite XAD® 1600 resin.

[0083] In practical practice, the mixture, adjusted to an approximately neutral pH value, is suitably purified by elution on Amberlite XAD® 1600 resin.

[0084] Alternatively, the mixture resulting from the adjustment of the solution pH to a lower value (e.g. 5-5.6) is preferably first eluted with a chelating resin such as Amberlite IRC748 or Diaion CR11 resin. The collected eluate is then preferably readjusted to a pH value of about 5.5-6 and concentrated, preferably at 50° C. under reduced pressure, to obtain an aqueous solution or mixture of dimeric complexes, preferably with a concentration of about 25% (w / w), which is then purified with Amberlite XAD® 1600 resin.

[0085] The collected fractions may then be treated with activated charcoal and filtered. The resulting filtered solution is then preferably concentrated, for example by distillation under reduced pressure at 45-55° C., to obtain a solution of dimeric complex 5 having a final concentration of about 25% (w / w).

[0086] Process h) The dimeric complex of formula 5 is then isolated according to step h). The complex can be isolated from the aqueous solution or mixture obtained in step g) for example by freeze-drying or by spray-drying. In a preferred embodiment, the desired dimeric complex is obtained as a white solid by spray-drying the solution recovered directly from step g) of the present process.

[0087] The overall yield of the present process, determined from the reactants defined as the free base DO3A tri-tert-butyl ester 1A, is at least 20%, preferably 25%, more preferably about 28%, or even >29%.

[0088] Interestingly, the method includes a step carried out in one pot, which is suitable for large-scale implementation and does not require isolation of either the prepared precursor (such as the compound of formula 1A) or the reaction intermediate. As a result, the objective of the synthetic approach of the present invention allows the overall yield of the final product to be increased by at least about 18% compared to the process disclosed in WO2017098044.

[0089] Additionally, the lack of isolation of intermediates allows for a reduction in overall process time.

[0090] Furthermore, the proposed process comprises the use of water, or more generally an aqueous solvent or aqueous solvent mixture, as reaction solvent in all steps subsequent to the preparation of the coupling product 3. In particular, when the compound of formula 3 is prepared in an organic solvent in step e), for example by reacting the compound of formula 2 obtained in step d) with DO3A tri-tert-butyl ester 1A obtained in step c), the organic solvent is replaced by an aqueous solvent or aqueous mixture by methods known to those skilled in the art, for example by first diluting an organic solution of the compound of formula 3 with water, a water / organic solvent mixture or an aqueous solution, and then optionally removing the organic solvent to obtain an aqueous solution of the compound of formula 3.

[0091] The use of an aqueous solvent or aqueous solvent mixture as reaction solvent in all steps following the preparation of the coupling is highly advantageous, especially in terms of cost, environmental impact and ease of implementation on an industrial scale. Indeed, the process disclosed in WO2017 / 098044 uses solvents such as DCM and materials such as TFA and TIPS, which are expensive and difficult to handle, especially when scaling up the process on an industrial scale. These solvents and materials may not be safe for the health of the workers. In contrast, the process of the present invention avoids or greatly reduces the use of organic solvents by using an aqueous solvent or aqueous solvent mixture in all steps following the preparation of the compound of formula 3, making it suitable and easy to implement for working on a large scale, for example for implementation in an industrial process. Furthermore, the process of the present invention surprisingly leads to very high yields of isolated dimeric complex, especially higher than the yields of the processes of the prior art, even when it involves the use of only an aqueous solvent or aqueous solvent mixture following the preparation of the compound of formula 3. The manufacturing process of the present invention also reduces the use of hazardous solvents and materials by using more aqueous solvents or aqueous solvent mixtures, and is therefore advantageous from cost, environmental and safety perspectives compared to prior art manufacturing processes.

[0092] All solvents and starting materials, including reactants such as epichlorohydrin, D-glucamine, and DO3A tri-tert-butyl ester hydrobromide salt, are either commercially available or can be obtained by known procedures.

[0093] In a preferred embodiment, the hydrobromide salt of DO3A tri-tert-butyl ester used as starting material for the preparation of the solution of ester 1A is prepared by using the preparation method described in patent application WO2021 / 116165 (of the same applicant as the present application) and exemplified below in the experimental section of this specification, and stored until use.

[0094] For the purpose of illustrating the invention in more detail, without limiting its scope, non-limiting examples of preferred embodiments of the manufacturing method of the invention are described in the following paragraphs.

[0095] Experimental Part Definitions of Abbreviations and Terms DO3A tri-tert-butyl ester (DO3A tBu): 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid tri-tert-butyl ester DO3A tri-tert-butyl ester-HBr (DO3A tBu-HBr): 1,4,7,10-tetraazacyclododecane-1,4,7-triacetate tri-tert-butyl hydrobromide TAZA: 1,4,7,10-tetraazacyclododecane tBuOK: Potassium tert-butoxide DMAC: N,N-dimethylacetamide DMC: dichloromethane DMF: Dimethylformamide DIPEA: N,N-diisopropylethylamine GdCl3: Gadolinium chloride HCl: Hydrochloric acid KOH: Potassium hydroxide ACN / MeCN: Acetonitrile NaOH: Sodium hydroxide Na2CO3: Sodium carbonate NH3: Ammonia MRI: Magnetic resonance imaging MeCN: Acetonitrile MTBE: Methyl t-butyl ether NMM: N-methylmorpholine K2CO3: Potassium carbonate TFA: Trifluoroacetic acid TIPS: Triisopropylsilane FLD: Fluorescence detector UV / Vis: Ultraviolet / Visible

[0096] HPLC characterization of the obtained compounds General Procedure Procedure 1: HPLC characterization and analysis of DO3A-tri-tert-butyl ester Chromatography conditions HPLC System A liquid chromatograph (eg Agilent 1100) equipped with a solvent delivery system, autosampler, column thermostat, degasser and a diode array or variable wavelength detector (or equivalent). Stationary phase: Zorbax Eclipse XDB-C 8, 5μm, 150×4.6mm Column temperature: 45℃ Mobile phase: A: 0.01M K2HPO4, 0.017M H3PO4 B: Acetonitrile Elution: Gradient Time (min) %B 0 5 30 80 35 80 38 5 45 5 Flow rate 1mL / min Temperature 45℃ Detection UV, 210nm, Bw=8nm; Reference 360nm, Bw=100nm Injection volume 10μL Downtime 35 minutes Reference peak DO3A 3tBu Retention time DO3A 3tBu approximately 14~15 minutes

[0097] Procedure 2: HPLC method to monitor the formation of intermediate 2 This method is utilized to monitor the mixture upon completion of alkylation of D-glucamine and after distillation of water. Chromatography conditions HPLC system: a liquid chromatograph (e.g., Agilent 1100) equipped with a solvent delivery system, autosampler, column thermostat, degasser, and a diode array detector or variable wavelength detector (or equivalent). Stationary phase: SeQuant ZIC-cHilic 3μm, 150×2.1mm (Merck PN1.50658.0001) Column temperature: 40℃ Mobile phase: Gradient elution Eluent A = 5 mM ammonium acetate Eluent B=ACN / MeOH, 75 / 25 Elution: Gradient Time (min) %B 0 97 5 97 30 20 40 20 45 97 60 97 Flow rate: 0.25mL / min Detection: UV, 210~240nm Injection volume: 10μL Duration: 60 minutes Dilute solution ACN / MeOH, 75 / 25 Sample preparation: Add 200 μL of 5 mM ammonium acetate solution to 75 μL of the mixture and dilute to 5 mL with diluent solution.

[0098] Procedure 3: HPLC method to monitor the formation and purification of intermediate 3 General Procedure This method is used to monitor the process of formation and purification of intermediate 3. Analysis conditions HPLC system Liquid chromatograph Agilent 1100 Stationary phase: Gemini, 5 μm, 250 × 4.6 mm (Phenomenex, item 00G-4435-EO) Column temperature: 40℃ Mobile phase: A: Mobile phase A B:MeCN Elution: Gradient Time (min) %B 0 40 5 40 30 90 35 90 36 40 45 40 Flow rate 0.7mL / min Detection UV / 210nm Injection volume 10μL Downtime 45 minutes INT 2 R t 21 minutes

[0099] Mobile phase A Preparation of solutions Accurately weigh 2.0 g of ammonium acetate into a 1000 mL volumetric flask, then dilute to volume with water. Transfer 600 mL of ammonium acetate solution and 300 mL of methanol to a 1000 mL volumetric flask. Sonicate for 30 minutes.

[0100] Procedure 4: HPLC method to monitor the formation and purification of chelating ligand 4 General Procedure The formation and purification of dimeric ligand 4 was monitored by reverse-phase HPLC with UV detection at 210 nm. Analysis conditions HPLC system Liquid chromatograph Agilent 1260 Infinity Stationary phase: Synergi Polar-RP, 4 μm, 150 × 4.6 mm (Phenomenex, item 00F-4336-EO) Column temperature: 40℃ Mobile phase: A: 10 mM KH2PO4 B: Methanol Elution: Gradient Time (min) %B 0 0 5 0 35 60 40 60 41 80 46 80 47 0 60 0 Flow rate 0.8mL / min Detection UV / 210nm Injection volume 10μL Downtime 60 minutes Compound 4 R t 2.4 minutes EXAMPLES

[0101] Example 1: Synthesis of DO3A-tri-tert-butyl ester hydrobromide The synthesis of the starting material DO3A tri-tert-butyl ester hydrobromide was carried out by using the procedure described in WO2021116165. Specifically: to a suspension of commercially available TAZA (14.39 kg; 83.53 mol) and sodium acetate (21.58 kg; 263.12 mol) in DMAC (98.07 kg; 104.33 L), a solution of tert-butyl bromoacetate (51.32 kg; 263.12 mol) in DMAC (50.72 kg; 53.96 L) was added at 10° C. for 2.5 hours. The temperature was then increased to 25° C. and the mixture was stirred at this temperature for 24 hours. Water (57.56 kg) was then added in 0.5 hours, and after 2 hours the mixture was centrifuged and washed with water (2×57 kg). The wet solid was dried under reduced pressure to give 36.62 kg; 61.48 mol of DO3A tri-tert-butyl ester hydrobromide (73.6% yield). The product has an assay (relative to a standard) of 100% w / w as determined by HPLC; an assay (relative to a standard) of 99.86% w / w as determined by NMR.

[0102] Example 2: Preparation of dimeric compound 5 Dimeric complex compound 5 was synthesized as follows: [ka] It is obtained by using the synthetic procedure shown and comprising the following steps: a) Conversion of salt 1B to DO3A tri-tert-butyl ester 1A DO3A 3t-Bu-HBr (236.68 g, 0.40 mol) was placed in the reactor. MTBE (350.29 g) was added and the mixture was thoroughly stirred. An aqueous solution of KOH (50.67 g of KOH in 710.05 g water, assay 88%, 0.80 mol) was charged to the suspension and the resulting mixture was kept at 23-27°C with stirring for 2 hours. After that, stirring was stopped and the mixture was separated into two layers, an upper organic layer and a lower aqueous layer. The aqueous phase was discarded and the organic phase was collected in the reactor. Quantitative yield. a1) Solvent exchange step with isopropanol Isopropanol (160.70 g) was added to the organic solution of Example 2a) and MTBE was completely removed by distillation. The assay of the final solution of DO3A 3tBu was in the range of 56-63% w / w. The assay of 1A in the solution was determined by HPLC-UV method.

[0103] b) Synthesis of intermediate 2 D-Glucamine (40.0 g; 0.221 mol) in water (99.3 g) was added dropwise over 2 h to a solution of epichlorohydrin (44.9 g; 0.486 mol) in DMAC (40.0 g; 0.043 L) at 24° C. After stirring the mixture for 17 h, DMAC was added (80.0 g; 0.085 L) and water was distilled under reduced pressure at 50° C. to give intermediate 2 in DMAC (residual water content <2.0% w / w).

[0104] c) Alkylation of Compound 1A with Intermediate 2 A solution of DIPEA (65.3 g; 0.505 mol) and 1A obtained according to Example 2 a2) is added at 50° C. to the solution of intermediate 2 recovered from Example 2 b). The mixture is further stirred at 70° C. for 72 h, while monitoring the conversion by HPLC-UV method, cooled to 25° C. and diluted with 16% w / w aqueous ammonia solution (0.240 L). The mixture obtained is stirred at 20° C. for 15 h, resulting in the precipitation of salts, which are removed by filtration. The filtrate is purified chromatographically on Amberlite XAD® 1600 (3 L; eluent: water / MeCN gradient). Pure fractions (HPLC area %≧90) are collected and distilled to remove the organic solvent. The residue obtained is concentrated under reduced pressure at 50° C. to obtain an aqueous solution of the protected ligand with a final concentration of about 10% w / w, which is used directly in the next step.

[0105] d) Deprotection of intermediate 3 Aqueous 34% hydrochloric acid (431.5 g; 4.023 mol) is added to the solution of intermediate 3 obtained in c) of Example 2, while keeping the temperature at 30-35 ° C. After the end of the addition, the mixture is heated to 37 ° C and stirred for 36 h. The solution is then cooled to 25 ° C, neutralized by adding aqueous 30% sodium hydroxide, tert-butanol formed as a by-product is removed by distillation and the mixture is desalted by nanofiltration. The mixture is then partially concentrated under reduced pressure at 50 ° C to a concentration of 24% w / w and chromatographically purified on Amberlite XAD® 1600 (1 L; water as eluent). The fractions selected by evaluation with HPLC-UV are treated with charcoal and concentrated under reduced pressure at 50 ° C to obtain a 10% w / w aqueous solution of the desired ligand 4 (0.075 mol) (quantified by potentiometric titration using aqueous copper sulfate as titrant).

[0106] e) complex formation The solution of deprotected ligand 4 obtained in Example 4 d) is heated to 37°C, and then an aqueous solution of gadolinium chloride (140.5 g of solution; 39.5 g of gadolinium chloride; 0.150 mol) is added, while maintaining the temperature in the range of 37-43°C. After the addition is complete, the pH is adjusted to 5.3 by adding 10% aqueous sodium hydroxide. The mixture is kept at 40°C for 2 hours, allowing the formation of the paramagnetic complex 5. The presence of free species is evaluated, for example by titration. The solution is then purified on Diaion CR11 chelating resin (0.16 L) to reduce the free gadolinium content. After loading, the resin is washed with water, the pH is adjusted to 5.5 and the solution is concentrated under reduced pressure at 50°C to obtain a 25% w / w aqueous solution. The solution is loaded onto Amberlite XAD® 1600 (3.3 L; eluent: water / MeCN gradient) at pH 6. Selected fractions, as assessed by HPLC-FLD and UV, are treated with charcoal and the resulting solution is distilled under reduced pressure at 50° C. The final solution (25% w / w) is spray dried to isolate the gadolinium complex as a white powder (82.0 g, equivalent to 74.6 g of anhydrous product; titration assay: 99% w / w%, anhydrous base). Overall yield from DO3A tri-tert-butyl ester 1A: 29%.

[0107] Example 3: Preparation of dimeric compound 5 The dimeric complex compound 5 can be obtained according to the synthesis procedure shown in Example 2 and the following steps: b) Synthesis of intermediate 2 D-glucamine (40.0 g; 0.221 mol) in water (100.0 g) was added dropwise over 2 hours to a solution of epichlorohydrin (44.9 g; 0.486 mol) in DMAC (40.0 g; 0.043 L) at 25° C. After stirring the mixture for 16 hours, DMAC (80.0 g; 0.085 L) was added and water was distilled under reduced pressure at 50° C. to obtain a solution of intermediate 2 in DMAC (residual water content <2.0% w / w).

[0108] c) Alkylation of Compound 1A with Intermediate 2 A solution of DIPEA (65.3 g; 0.505 mol) and 1A obtained in a2) of Example 2 is added to the solution of intermediate 2 recovered from step b) of Example 3 at 50° C. The mixture is further stirred at 75° C. for 70 h while monitoring the conversion by HPLC-UV and then partially concentrated under reduced pressure at 60° C. After cooling to 23° C., a previously prepared mixture of water (80.0 g) and MeCN (126.4 g; 0.160 L) and 25% w / w aqueous ammonia solution (144.5 g; 0.160 L) are added. The resulting mixture is stirred for 14 h at 22° C. The mixture is filtered and purified chromatographically using Amberlite XAD® 1600 (3 L; eluent: water / MeCN gradient). After elution, fractions with appropriate purity (HPLC Area % ≥ 90) were collected, the organic solvent was removed by distillation, and the resulting solution was concentrated under reduced pressure at 50 °C to give an aqueous solution of the protected ligand 3 (concentration: 13% w / w), which was used directly in the next step.

[0109] d) Deprotection of intermediate 3 Aqueous 34% hydrochloric acid (435.0 g; 4.057 mol) is added to the solution of intermediate 3 obtained in step c) of Example 3, while keeping the temperature at 30°C to 35°C. After the addition is complete, the mixture is stirred at 35°C for 32 hours. The solution is then cooled to 23°C, neutralized by adding aqueous 30% sodium hydroxide, the t-butanol formed as a by-product is removed by distillation, and the mixture is desalted by nanofiltration. The mixture is then partially concentrated under reduced pressure at 50°C to a concentration of 22% w / w and purified chromatographically on Amberlite XAD® 1600 (1 L; eluent: water). The fractions selected by HPLC-UV evaluation are treated with charcoal and concentrated under reduced pressure at 50°C to obtain a 25% w / w aqueous solution of the desired ligand 4 (0.076 mol) (quantified by potentiometric titration using aqueous copper sulfate as titrant).

[0110] e) complex formation To the solution of deprotected ligand 4 at 25 °C, an aqueous solution of gadolinium chloride (142.4 g of solution, 40.1 g of gadolinium chloride, 0.152 mol) is added, keeping the temperature in the range of 23-27 °C, and the pH is adjusted to 7.0-7.5 by adding 30% aqueous sodium hydroxide. The mixture is kept at 25 °C for 24 h, allowing the formation of the paramagnetic complex 5. The presence of free species is evaluated, for example, by titration. The resulting solution is purified on an Amberlite XAD® 1600 (3.3 L, eluent: water / MeCN gradient). The fractions selected by evaluation by HPLC-FLD and UV are treated with charcoal, and the resulting solution is distilled under reduced pressure at 50 °C. The final solution (25% w / w) is spray-dried to isolate the gadolinium complex as a white powder (73.5 g, corresponding to 66.9 g of anhydrous product; titration assay: 99% w / w%, anhydrous base). Overall yield from DO3A tri-tert-butyl ester 1A: 26%.

[0111] Results similar to those of Examples 2 and 3 above can be obtained, for example, by carrying out procedures similar to those disclosed in co-pending application PCT / EP2021 / 070801.

Claims

1. A method for producing a dimer complex compound 5 represented by the formula 【Chemical 1】 comprising the following steps: a) A base aqueous solution and an organic solvent immiscible with the base aqueous solution are mixed with a salt represented by the formula 1B 【Chemical Formula 2】 [wherein X is a halogen anion and y is an integer of 1 to 3] to obtain a heterogeneous mixture containing the salt of formula 1B; b) converting the salt of step a) to obtain a heterogeneous mixture containing the DO3A tri-tert-butyl ester represented by the formula 1A [Chemical Formula 3] ; c) recovering the organic solvent from the heterogeneous mixture of step b) to obtain an organic solution containing the DO3A tri-tert-butyl ester of formula 1A; d) preparing a solution containing the compound represented by the formula 2 【Chemical Formula 4】 in an organic solvent; e) mixing the solutions of steps c) and d) to obtain a solution containing the compound represented by the formula 3 [Chemical Formula 5] ; f) removing the tert-butyl protecting group from the compound of formula 3 without isolating the compound from the solution of step e) to obtain a solution containing the respective free ligand represented by the formula 4 [Chemical Formula 6] ; g) adding gadolinium metal ions to the solution of step f) without isolating the free ligand of formula 4 to obtain a solution containing the dimer complex of formula 5; and h) isolating the dimer complex wherein the reaction solvent in all steps following the preparation of the compound of formula 3 is an aqueous solvent.

2. The production method according to claim 1, wherein the organic solvent in step a) is ether, preferably methyl tert-butyl ether (MTBE).

3. The production method according to claim 1 or 2, wherein the amount of the organic solvent in step a) is 1.0 to 5.0 w / w based on the amount of the salt 1B.

4. The production method according to claim 3, wherein the amount of the organic solvent in step a) is 1.2 to 3.0 w / w based on the amount of the salt 1B.

5. The production method according to claim 4, wherein the amount of the organic solvent in step a) is 1.4 to 1.6 w / w based on the amount of the salt 1B.

6. The production method according to claim 5, wherein the amount of the organic solvent in step a) is 1.5 w / w based on the amount of the salt 1B.

7. The basic aqueous solution contains a base, preferably an inorganic base, more preferably KOH, NaOH, Na ２ CO ３ and K ２ CO ３ The production method according to claim 1 or 2, comprising an inorganic base selected from the group consisting of

8. The production method according to claim 7, wherein the base has a molar ratio of 1.0 to 4.0 moles per mole of the salt 1B1.

9. The production method according to claim 8, wherein the base has a molar ratio of 1.2 to 3.0 moles per mole of the salt 1B1.

10. The production method according to claim 9, wherein the base has a molar ratio of 1.7 to 2.3 moles per mole of the salt 1B1.

11. The production method according to claim 10, wherein the base has a molar ratio of 2.0 mol to 1 mol of salt 1B.

12. The production method according to claim 1 or 2, wherein the amount of the basic aqueous solution in step a) is 2.0 to 10 w / w based on the amount of salt 1B.

13. The production method according to claim 12, wherein the amount of the basic aqueous solution in step a) is 2.2 to 6.0 w / w based on the amount of salt 1B.

14. The production method according to claim 13, wherein the amount of the basic aqueous solution in step a) is 2.8 to 3.2 w / w based on the amount of salt 1B.

15. The production method according to claim 14, wherein the amount of the basic aqueous solution in step a) is 3.0 w / w based on the amount of salt 1B.

16. The production method according to claim 1 or 2, wherein y of salt 1B in the above formula is 1 and / or X of salt 1B in the above formula is a bromide ion.

17. The production method according to claim 1 or 2, wherein step d) includes reacting D-glucamine with epichlorohydrin to obtain a solution containing the compound of formula 2 in an organic solvent.

18. d1) Adding an aqueous solution of D-glucamine to a solution containing epichlorohydrin in an organic solvent to obtain the compound of formula 2 in a water / organic solvent mixture; preferably, the amount of epichlorohydrin is a slightly excessive amount exceeding the stoichiometric amount; and d2) Removing water from the mixture to obtain a solution containing the compound of formula 2 in an organic solvent The production method according to claim 17, which includes.

19. Step e) is e1) Reacting the compound of formula 2 obtained in step d) with the DO3A tri-tert-butyl ester 1A obtained in step c) in the presence of a base to obtain a crude organic solution; e2) Diluting the obtained crude organic solution with water, a water / organic solvent mixture, or an aqueous solution to obtain a water / organic crude product; e3) Purifying the water / organic crude product, preferably by chromatography, to obtain the compound of formula 3 in a water / organic solvent mixture; and e4) Removing the organic solvent from the mixture to obtain an aqueous solution containing the compound of formula 3 The production method according to claim 1 or 2, which includes.

20. The production method according to claim 19, which includes adding an aqueous solution to the water / organic crude product of step e2) generated by diluting the crude organic solution with a water / organic solvent mixture.

21. Step f) includes the following: f1) adding an acid to an aqueous solution containing the compound of formula 3 obtained in step e) to remove the tert-butyl protecting group to obtain an acidic solution containing the free ligand of formula 4; f2) adding a base to the acidic solution to obtain a substantially neutral aqueous solution containing the free ligand; and f3) after purifying the obtained neutral solution, optionally concentrating it to obtain an aqueous solution containing the free ligand of formula 4 The production method according to claim 1 or 2, comprising the above steps.

22. Step f3) comprises distilling the neutral solution to remove the produced t-butanol; desalting the distillation residue; purifying the desalted solution by chromatography to obtain an aqueous solution containing the ligand of formula 4; and optionally concentrating the aqueous solution The production method according to claim 21, comprising the above steps.

23. Step g) comprises g1) adding a gadolinium salt to the solution containing the ligand of formula 4 obtained in step f) to obtain a solution containing the dimer complex of formula 5; g2) purifying the solution, preferably by chromatography, to obtain a solution containing the dimer complex; and g3) concentrating the solution The production method according to claim 1 or 2, comprising the above steps.

24. Step h) comprises isolating the dimer complex of formula 5 as a white solid by spray drying the solution directly recovered from step g). The production method according to claim 1 or 2, comprising the above step.

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